1. Field of the Invention
The present invention relates to a method of producing composite clusters, wherein a metal is lamellarily compounded with a semiconductor or nonconductor, useful as various functional elements, and also relates to an apparatus for production of such composite clusters.
2. Description of the Related Art
Aggregate of fine particles are useful as functional elements, e.g. gas sensors and permselective membranes, in various industrial fields due to its big specific surface area and good affinity with an atmospheric gas.
Various methods have been proposed so far for producing aggregate of fine particles. For instance, starting material is evaporated and condensed to fine particles in vapor-phase synthesis. According to a colloidal process, fine particles are precipitated from an electrolytic liquid and stabilized with a surfactant. An aerosol process for spraying and pyrolysis of a metal ion-containing liquid, a gas-atomizing process for spraying a mixture of molten metal with an inert gas through a nozzle, and a milling process for mechanically crushing solid material are also proposed for production of such aggregate.
The aerosol process, the milling process and the gas-atomizing process are advantageous for mass-production of clusters but unsuitable for production of clusters, which have particle size conditioned to nanometer order for performance originated in nano-sized particles. The colloidal process can not avoid inclusion of impurities in a product, although clusters of several nanometers in particle size can be mass-produced. The inclusion of impurities degrades quality of the product.
On the other hand, the vapor-phase process promotes growth of clusters in a clean vacuum atmosphere without invasion of impurities. The clusters produced by the vapor-phase process has a chemically active surface effective for improvement of functionality. However, the active surface causes unfavorable oxidation and coalescence of clusters, when fine particles are deposited on a substrate. The oxidation and coalescence impede realization of the functionality originated in nano-sized particles, regardless of very fine clusters.